Aim To investigate the relationship between endothelium dependent vascular relaxation (EDVR) and endothelin at different stages of rats with non-insulin-dependent diabetes mellitus (NIDDM). Methods The rat models of NIDDM were made. At 10 and 25 weeks after injecting STZ, the contents of plasma endothelin were measured respectively with radioimmunoassay, and EDVR actions were studied by isometric tension recording in the isolated aorta rings. Results At 10 weeks of NIDDM rats, the EDVR responses of aortae were obviously weakened and the level of plasma markedly ascended, comparing with normal placebo group. At 25 weeks of NIDDM rats, the EDVR respondes of aortae were further imparired, but the level of plasma endothelin descended and was lower than the NIDDM rats of 10 weeks (p<0.05). Conclusions The results suggest that weakened EDVR may be related to the increased content of endothelin at early stage of NIDDM rat, but impaired EDVR may have nothing to do with endothelin at late period.